1. Technical Field of the Invention
The present invention relates to devices for protecting integrated electrical circuits against electrostatic discharges. It relates more particularly to such protection devices comprising several thyristors or, equivalently, one thyristor produced in segmented (“multi-finger”) form. For the case in question, that of protecting integrated electrical circuits, the protection device is incorporated into the same substrate as the protected circuit.
2. Description of Related Art
Many electrical circuits, depending on their use, their sensitivity or their installation, need to be protected from being damaged by possible electrostatic discharges. Such discharges are caused, for example, by an operator touching part of an electrical circuit without taking particular precaution.
The document entitled “A synthesis of ESD input protection scheme” by Ch. Duvvury and R. Rountree, Journal of Electrostatics, 29 (1992), pp 1–19, describes various designs of electrostatic discharge protection devices. Some of these devices use the avalanche effect of an electrical junction placed in a semiconductor substrate or the snapback effect of an MOS transistor to open a pathway for draining away the electrical charges of an electrostatic discharge. Moreover, this draining pathway commonly comprises a thyristor or silicon-controlled rectifier (SCR).
A drawback of this type of electrostatic protection based on avalanche or snapback effects is due to the fact that the thresholds at which these effects appear depend on the densities of the electrical dopings produced. Such protection means become inefficient when these thresholds are too high in relation to certain characteristics of the electrical circuits to be protected. Various improvements to these protection means have been proposed, but they result in complex combinations of electronic components.
In addition, some electrostatic discharges may correspond to particularly large quantities of electric charges, such that a single drain pathway may be insufficient to provide effective protection of the electrical circuit.